In order to satisfy a high-reliability requirement, a storage system designed for business applications may be provided with a plurality of processors for issuing IO requests to a control processing apparatus, which is used for controlling disks, on the basis of the requests received from clients. These processors supervise each other. If a failure occurs in one of the processors, another processor serves as a substitute for the failing processor, doing jobs supposed to be done by the failing processor so that the storage system is capable of continuing its normal operations. In the mutual supervision among the processors, communications referred to as heart beats are generally carried out to periodically exchange information such as the present time. When a response in a heart-beat communication is lost for a predetermined period of time, the processor not giving the response is considered to be in a down state. In this case, a transfer of jobs is made. In addition, exchanges of information are not limited to the heart-beat communications. For example, a lot of data known as system configuration information is communicated among internal processors. In these communications, data is generally exchanged by way of an external network. There is a method of carrying out internal communications by using an internal network instead of an external network. It is difficult, however, to lay a internal network capable of operating at a very high speed due to space problems.
By the way, if an external network is used for inter-processor communications in a storage system employing a plurality of processors as described above, communicated data may inevitably flow to an undesirable external destination, making the communications between the processors prone to problems of security. If an external network is not used, on the other hand, it is necessary to specially connect a dedicated network inside the storage system. However, such an internal network incurs a cost that would otherwise be not required.
It is thus an object of the present invention to implement secure communications for exchanging data by way of a disk cache, which can be accessed by a plurality of processors as a cache common to the processors, with neither using an external network nor newly laying a dedicated network.
Japanese Patent Laid-open No. 2002-23958 discloses a conventional technology for carrying out communications among a plurality of processors by way of a disk cache. In accordance with a communication technique based on this conventional technology, a mainframe host places communicated information in the disk cache and an open system host fetches the information from the disk cache. In this communication technique, the mainframe host and the open system host pertain to different systems. This communication technique may raise a problem of security in that the open system host is connected to the disk cache by an external network. In addition, communications can be carried out only on the direction from the mainframe host to the open system host so that duplex communications are impossible.